This invention relates to a prosthesis bearing component which can be utilized, for example, in a prosthetic hip socket.
Ultra-high molecular weight polyethylene (UHMWPE) has been used as a bearing surface for acetabular components and coupled with a metal or ceramic femoral head this material has shown excellent resistance to penetration wear. However, advances it total hip arthroplasty have shown that, although such sockets very rarely wear through, debris can be generated form it which can cause adverse tissue reactions.
In two papers published by Elsevier Science Ltd. in 1999 entitled xe2x80x9cSuitability and limitations of carbon fiber reinforced PEEK composites as bearing surfaces for total joint replacements (A. Wang, R. Lin, C. Stark and J. H. Dumbleton) Tribiology International, Vol. 31, No. 11, pp 661-667, and xe2x80x9cCarbon fiber reinforced polyether ether ketone composite as a bearing surface for a total hip replacementxe2x80x9d (A. Wang, R. Lin, V. K. Polineni, A. Essner, C. Stark and J. H. Dumbleton) Wear (1999), Volume No. 225/229, pp. 724-727, the possibilities and advantages of using carbon fiber reinforced polyether ether ketone (PEEK) composite as a bearing surface for total replacements id discussed and analysed. These papers describe the manufacture of acetabular cups made from carbon fiber reinforced PEEK composite and conclude that such cups offer advantages over UHMWPE composite cups.
A carbon fiber reinforced composite acetabular cup is shown in U.S. Pat. No. 5,609,646 and a composite hip implant is shown in U.S. Pat. Nos. 5,181,930 and 5,443,513.
Further research now shows that even further advantages can be obtained with carbon fiber composite cups if certain steps are taken during manufacture.
According to the present invention a prosthetic bearing component is formed from a composite synthetic plastics material comprising an injection molded thermoplastic polymeric matrix reinforced by a pitch based carbon fiber and having a bearing surface which has been machined with an average surface roughness with a value less than an Ra of 2 xcexcm. Such components have shown superior wear qualities.
Preferably the bearing surface shape is machined with tolerances of 0.1 to 0.15 mm. The composite material must be capable of withstanding a radiation value of at least 2.8 Mega Rads (MRad) without degradation. Such radiation may be for sterilization purposes. In components in which the bearing surface is substantially or part spherical a sphericity of 0.3 xcexcm within a solid angle of 45xc2x0 is required.
The thermoplastic polymeric matrix can be a polyester, for example PVT (polyethylene tetraphthalate), a polyonylketone, for example PEEK (polyether ether ketone), or a polysulphone, for example polyethersulphone. It is also possible that other materials can be employed.
The bearing component can be in the form of a cementless bearing element having an outer surface which includes a number of raised engagement features.
These features can be provided in directions extending away from and/or towards the outer periphery of the outer surface and can be formed by projecting strakes of substantially triangular cross-section. Moreover, the outer surface can also carry one or more projecting fins.